Imported model not there
There are multiple reasons that the object is not visible after importing.


Check the outliner and see if there is an object. Also see if it's visibility is on.
Make sure you are in the correct layer. To display objects from all layers in the 3D view, press the backtick key.
The camera clipping planes must not be proper. If you are looking from the User Persp camera, press the N key and adjust the Start and End values for the Clip plane. If you are looking from a camera object, edit the clip start/end in the camera data properties.
In most cases pressing SHIFT+C in the viewport should frame all the objects in the scene. Refer to point 2 if 1 and 3 still does not fix the problem.